The document U.S. Pat. No. 6,185,240 B1 describes a laser diode with a second diode connected anti-parallel with it. The second diode in this case represents protection against electrostatic discharge (ESD) for the laser diode. This protects the laser diode against ESD voltage pulses, which can occur in the reverse-biased direction of the laser diode.
The document U.S. Pat. No. 5,914,501 describes a light-emitting diode arrangement with a secondary connecting element, which forms ESD protection for the light-emitting diode. The secondary connecting element is connected in parallel with the light-emitting diode and protects the light-emitting diode by dissipating electric current from the light-emitting diode and by thus limiting the voltage which is applied to the light-emitting diode in the reverse-biased direction to a specific maximum value. The secondary connecting element may, for example, be a zener diode.